28 Lamarck's Genera of Shells: 



form, but it is more nearly allied to the chama, in which genus 

 Bruguiere has included it. It differs from them, however, by 

 its hinge, and the singular form of the beaks. 



Only one species. Diceras arietinum*. (Chama bicornis. 

 Brug.) 



Fossil, from Mont Sal^ve. France, PI. I. Fig. 73. 



2. Chamat. 



Shell irregular, inequivalve, fixed; beaks curved, unequal. 

 Hinge with only one thick, oblique, subcrenate tooth, fitting 

 into a pit on the opposite valve. Two distant, lateral, muscu- 

 lar impressions. Ligament external, depressed. 



In the genus chama Linnaeus has included very dissimilar 

 shells, uniting regular and equivalve shells with those that arc 

 irregular and inequivalve, and free shells with fixed. Bruguiere 

 reformed this genus, which now consists of irregular, coarse, 

 rough, scaly or spinous shells, with very unequal valves, and 

 only one thick, oblique, transverse, callous tooth, usually crenate 

 or furrowed. The beaks are curved inwards, and only one of 

 them projects at the base of the shell. 



The chamte usually live in shallow salt water; they are 

 always found attached to rocks, or corals, by the larger valve, 

 or adhering together in various groups : except the scaly or 

 lamellar species, they are seldom brilliantly coloured. This 

 genus is subdivided into (1) shells, whose beaks turn from left 

 to right, 10 species ; and (2) those from right to left, 7 species. 

 Type. Chama lazarus. CIdem, Linn.) 



Shell imbricate ; lamellae dilated, wavy-plicate, sublobate, 

 obsoletely striated. American Ocean. In all, 17 recent spe- 

 cies, and 8 fossil. PI. I. Fig. 74. 



3. Etheriaj. 



Shell irregular, inequivalve, adhering ; beaks short, sunk, as 



* Of, or behtiging to, a ram. 



t Chama, the Latin name of a species of shell fish, said to be derived 

 from x"'"") *o gape, 

 i One of the oceunides, or sea-nymphs. 



